im currently running this setup myself and i went 4 demonology warlocks and 1 holy priest with a few points in discipline for reduced threat. Its been working out VERY well for me, typicaly i send in 4 felguards instant corruption and wand and the mobs die within probably the first 2-3 wand shots.

Im going to be twinking out this current team for 60-69 bracket and will most likely go affliction once i start to pvp